Abstract
Recycling rare-earth elements from Nd magnet scrap (Nd–Fe–B scrap) is a highly economical process; however, its efficiency is low due to large portions of Fe impurity. In this study, the effective separation of Fe impurity from scrap was performed through an integrated nitric acid dissolution and hydrothermal route with the addition of fructose. Results showed that more than 99% of the scrap was dissolved in nitric acid, and after three dilutions that the Nd, Pr, Dy and Fe concentrations in the diluted acid were 9.01, 2.11, 0.37 and 10.53 g/L, respectively. After the acid was hydrothermally treated in the absence of fructose, only 81.8% Fe was removed as irregular hematite aggregates, whilst more than 98% rare-earth elements were retained. By adding fructose at an Mfructose/Mnitrate ratio of 0.2, 99.94% Fe was precipitated as hematite nanoparticles, and the loss of rare-earth elements was <2%. In the treated acid, the residual Fe was 6.3 mg/L, whilst Nd, Pr and Dy were 8.84, 2.07 and 0.36 g/L, respectively. Such composition was conducive for further recycling of high-purity rare-earth products with low Fe impurity. The generated hematite nanoparticles contained 67.92% Fe with a rare-earth element content of <1%. This value meets the general standard for commercial hematite active pharmaceutical ingredients. In this manner, a green process was developed for separating Fe from Nd–Fe–B scrap without producing secondary waste.
Highlights
Nd magnet scrap (Nd–Fe–B scrap) is a common material in the collection of magnetic products in the permanent magnet industry [1]
Fe impurity in the acid solution of scrap was successfully separated via a one-step hydrothermal route with fructose as the auxiliary reagent
Fructose was oxidised by nitrate with the involvement of H+ in the acid, steadily increasing the acid’s pH and enhancing the hydrolysis of ferric Fe to hematite with FeOOH as the intermediate
Summary
Nd magnet scrap (Nd–Fe–B scrap) is a common material in the collection of magnetic products in the permanent magnet industry [1] This scrap is composed of approximately 30% rare-earth elements and 50–70% Fe impurity [2]. Numerous approaches for recycling rare-earth elements from scrap have been developed, including selective precipitation [4], solvent extraction [5,6,7,8,9] and cationic exchange [1]. Önal et al [4] dissolved scrap in sulphuric acid and found that ferrous Fe in the acid was oxidised to ferric Fe by adding MnO2 and precipitated as Fe oxyhydroxide when the acid was adjusted to pH 3 using Ca(OH)2 In this process, approximately 23% of the rare-earth elements were lost. Unlike the 2.5 g/L Fe that was residual in the conventional method, less than 10 mg/L Fe was kept with the new hydrothermal route, while only less than 2% rare-earth elements were lost
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
